Scrap recovery process

ABSTRACT

THE RECOVERY OF METAL VALUES IN SCRAP MATERIALS BY DESTRUCTIVE DISTILLATION REMOVAL OF ORGANIC NON-METAL MATERIALS, AT TEMPERATURES WHICH LEAVE THE METAL RELATIVELY UNAFFECTED.

1972 J. E. PERRY 3,697,257

SCRAP RECOVERY PROCESS Filed Nov. 7, 1969 FURNACE FOR HEATING SCRAPMATERIAL AND DESTRUCTIVELY DISTILLING ORGANIC MATERIAL IN SAME INVENTORJohn E. Perry B ,idm

ATTORNEY United States Patent Office 3,697,257 Patented Oct. 10, 19723,697,257 SCRAP RECOVERY PROCESS John E. Perry, Bay Village, Ohio,assignor to Horizons Research Incorporated Filed Nov. 7, 1969, Ser. No.874,891 Int. Cl. C2211 25/06 US. C]. 75-64 6 Claims ABSTRACT OF THEDISCLOSURE The recovery of metal values in scrap materials bydestructive distillation removal of organic non-metal materials, attemperatures which leave the metal relatively unaffected.

This invention relates to the recovery of metal values in scrapmaterials in which the metal values are associated with non-metallicmaterials, such as insulation on scrap wire.

Among the methods which have been suggested for recovering the metalvalues separately from the non-metal associated therewith areincineration or burning of combustible material, such as plastics,rubber, resin or paper, carried on the metal, which it is desired toreclaim. Such methods require an oxidizing atmosphere and usually arecarried out at relatively high temperatures. As a consequence,substantial amounts of the metal are oxidized with consequent loss ofmetal product salvaged as metal.

Another method which has been suggested involves heating metal scrap andthe non-metallic materials found with it in a retort or closed chamber.Such a procedure requires the treatment of small batches of product andis inherently more expensive than a process in which the material isprocessed continuously in an orderly manner through a suitableapparatus.

These and other suggested procedures in which the materials are exposedto relatively high temperatures are objectionable for at least tworeasons. First, because the metal is contaminated by oxidation andsecond because the physical properties of the metal which is laterrecovered are usually adversely affected by the overheating, and are,therefore, not as good as those possessed by the metal before it wasprocessed for removal of the undesired organic or inorganic materialswhich may be considered as contaminating the metal to be recovered.

One object of the present invention is to provide a process in whichwaste materials associated with metal scrap are continuously removedfrom the metal by a simplified, continuous process which avoids thesmoke generated and overheating accompanying combustion processes, andin which the metal is recovered in a relatively uncontaminated statewhile it retains its physical properties and in which the major portionof the contaminating non-metallic material is recovered as a volatile orcondensible gaseous product which is useful as a fuel or heating means.

Briefly, the method of the present invention consists of heating thecontaminated scrap, in the absence of oxygen, to a temperature at whichall of the volatile components are distilled off, using a continuousfeed and removal of residue. At the temperatures involved, some volatilecomponents are formed by destructive distillation. The volatilecomponents, liquid and gas fractions, may be collected for reuse or theymay be ignited and burned with a smokeless, odorless flame.

Another object of the invention is to provide an ap paratus for carryingout the above described process, which apparatus includes:

a furnace in which scrap is heated in the absence of any appreciableamounts of oxygen to temperatures at which all of tthe volatilecomponents are distilled from the metal scrap itself;

means for continuously introducing scrap to be processed into thefurnace and for removing scrap from the furnace after it has beenprocessed, said means including equipment for recovering those portionsof the scrap which melt during the heating;

a flame curtain at the entrance end of the furnace, or other means forprotecting the furnace atmosphere from contamination by air or oxygen;

a discharge chute at the exit end of the furnace, through whichprocessed scrap, solid non-metal residue and furnace atmosphere all flowdownwardly; and

means to separately collect and recover the processed scrap, anynon-metal solid residue and any gaseous products produced as a result ofpassage of the charge through the furnace.

The aapparatus may also include auxiliary means to enhance the recoveryof a more saleable, e.g. less contaminated metal product including suchdevices as means for crushing, sieving and other devices for physicallyseparating metal from non-metal, and other means for improving the formof product including cleaning means and/or melting means, if suchadditional treatments are found to be economically desirable.

By means of appropriate seals at the inlet and outlet of a heated zone,a continuous feed is carried through the heated zone, and thedistillation takes place in an inert atmosphere at atmospheric pressure.At start up, an inert gas, such as nitrogen, is used to purge the heatedzone of air. After the reaction starts, the gas formed by thedestructive distillation furnishes an oxygen-free atmosphere.

When the contaminants associated with the metal scrap are organicmaterials, such as rubber or synthetic resins or paper, the residuewhich remains on the metal scrap after heating is usually a light-weightdry coke. When the coke is separated from the metal and recovered, thecoke may be used as a clean fuel or as a land fill or in any othersuitable way.

When the contaminants associated with the metal scrap are inorganicmaterials, such as asbestos or fiberglass, the residue becomes brittleand can be readily detached from the metal scrap which remains virtuallyunaffected.

A special situation exists when the contaminants to be removed from themetal scrap include materials, such as tin or solder which melt at theusual operating temperature. When such materials are accompanied bysubstantial amounts of organic material, the tin or solder is usuallytaken up by the coke residue, from which the tin or solder can berecovered by incinerating the coke in an oxidizing atmosphere.

The metal scrap, after the heating step, is processed to effect physicalseparation of the residue still attached to the scrap metal, from thatmetal, e.g. by action of heaters, brushes or scrapers, or by exposure tosound waves or any other known means for physicaally detaching the majorpart of the residue (coke, char, glass or tin containing coke) from themetal scrap, the recovery of which is the object of the process.

In order to remove the last traces of residue from the metal scrap, itis then passed through a fused salt bath, as hereinafter described, thecomposition of the fused salt being such that the coke or any otherorganic residue is oxidized at a relatively low temperature.

Thereafter the metal scrap is withdrawn from the salt bath and after thesalt has been permitted to drain from the metal scrap, the scrap can bewashed or rinsed, or recovered as it stands.

The invention will be more fully understood from a consideration of thedescription which follows taken in conjunction. with the drawings inwhich a schematic apparatus for carrying out the invention is shown.

As shown, the apparatus includes a furnace which may be similar to aconventional powder metallurgy furnace or a rotary furnace. Furnace 10has an inlet end 12 and an outlet end 14, and is provided with aconveyor 16, for example, a stainless steel belt for carrying scrapmaterial through the furnace. Furnace 10 is provided with means tosupply heat to the furnace for start-up and for maintaining thetemperature of the furnace substantially constant at a controlled levelduring operation. A flame curtain 18 is provided at the inlet end of thefurnace to keep air out of the furnace and to maintain a non-oxidizingatmosphere in the furnace 10. Gases produced by the destructivedistillation in furnace 10 burn at the flame curtain 18 at the inletend.

From the furnace, the product discharged at the outlet end 14 fallsthrough a chute 20. Beneath the chute 20 is a hopper 24 with a bottomdischarge through a star value 26 and a side discharge through a sidearm 28.

As noted above, the scrap product emerging from the outlet end 14 offurnace 10 usually carries a coke or ash like residue which adheres tothe metal. This may be detached from the metal by means located in chute20, such as a rolling ring crusher 30, or by other physical means. .Thescrap and loosened char fall onto a vibrating screen 34 which permitsthe coke-like residue to fall free of the metal to a collection bin. Themetal, with any remaining residue, is conveyed from the screen 34 to aheated fused salt bath 40, such as is described in U.S. Pat. No.3,000,766 and in U.S. pending application, Ser. No. 804,018,filed Mar.3, 1969 and now U.S. Pat. 3,615,815, issued on Oct. 26, 1971.

After the furnace is started and before raw material is put through on acontinuous belt or continuous bucket conveyor, an initially neutralatmosphere can be provided consisting of gases such as nitrogen,hydrogen, cracked ammonia, and/or carbon dioxide. As soon as the organicmaterial on its wire starts to pyrolyze, is substantially all cases, thegaseous products of the pyrolyzed organic material will form aprotective atmosphere whch is nonoxidizing in character, since themajority of organic insulation is usually composed of synthetic resin orpaper, or natural resins.

The gases evolved provide the necessary controlled atmosphere. As muchas 90% or more of the usual organic insulation is charred anddestructively distilled in a matter of minutes in a temperature rangebetween 900 F..

and 1500 F., and the char formed is easily detached from the metal, asindicated above. As such temperatures, the metal is not oxidizedappreciably, nor is it adversely affected by the brief heating to whichit is subjected.

The coke was removed from the wire with a rolling ring crusher and themixture was separated on a vibratory screen. The screen was formed of aperforated sheet with A" holes.

The product was of uniform quality independent of diameter of wire;gauge sizes tested varied from No. 6 to No. 25. A slight discolorationon the wire was removed in the salt bath. Only a slight reaction wasnoted when the wire was placed in the salt bath and the reaction wascomplete in less than a minute.

It should be noted that the operating temperature is above the meltingpoint of lead. Lead sheathed wire may be fed to the furnace and the leadremoved by melting. The mechanism for removal of lead from the furnacewould be the belt 38 which would be designed with buckets to collect themolten lead and deposit the metal on the inlet end of the furnace. Thisadditional feature is shown schematically in the drawing, at 44.

The second conveyor 38 positionedbeneath conveyor 16 in furnace 10catches nonagaseous products formed when the insulation and othercoating materials burn off the wire and discharges them at the inlet endof the furnace.

Crushing and screening should be done while the metal scrap, e.g. wire,is hot to conserve heat at the salt bath. These operations would be donein the atmosphere of the furnace. Coke is removed through a star(rotary) valve 26 and metal or wire is conducted into the salt bath 40into which it passes below the surface of the salt. A continuousconveyor 42 removes the wire from the salt bath and discharges the wireproduct into a container 48.

The method is described more fully in the following example.

Feed material was from representative samples of insulation wire. Theinsulation material included polyvinyl chloride, neoprene, paper, cloth,rubber, polyethylene, fiberglass, and various varnishes and waxes. Thefeed was cut to a size to produce a free flowing mixture. Each of theinsulation materials was treated in the above described apparatus,separately and then in mixtures; no diflerence was found in reactivityof the organic materials under the conditions of operation specifiedabove, ie, absence of oxygen and at temperatures at which organicmaterials were destructively distilled.

In a series of runs in which tin coated copper wire was processed, thentin content of the coke residue averaged about 0.32 weight percent. Thetin was completely removed from the copper wire by maintaining thefurnace temperature at 850 F. or higher. At higher temperatures, such as1200 F., the tin is completely removed in as short a residence time infurnace 10 as 1.5 minutes. Similar results were obtained for the removalof lead solders from soldered scrap, by melting the solder.

It is also to be noted that the furnace 10 includes two parallelconveyors, one disposed above the other. These run in oppositedirections so that scrap being processed is conveyed by the upper run ofthe uppermost conveyor away from the entry end and towards the dischargeend of the furnace, while separated material is conveyed by the upperrun of the lowermost conveyor towards the entry end and away from thedischarge end of the furnace.

Also the evolution of gas during the distillation process results in anexcess of gas in the furnace and some gas passes down into hopper 20 andout valve 22 when it is opened, further protecting the furnace fromcontamination by air or oxygen.

The metal product may be recovered without crushing or sieving or fusedsalt cleanup, if desired, or it may be melted or otherwise processedwithout departing from the spirit of the present invention.

From the foregoing it will be readily seen that the process andapparatus of this invention may be applied to a wide spectrum of wastematerials from which it is desired to reclaim the metal values.

I claim:

1. A continuous process for the recovery of metal values from a scrapmaterial consisting of (1) the metal values to be recovered and (2)contamination selected from the group consisting of organic material,inorganic materials including metals, and mixtures of organic andinorganic materials, which comprises:

continuously charging said scrap material into a furnace;

conveying said scrap material through said furnace while heating saidscrap material in said furnace in the absence of any substantial amountsof oxygen, said heating being to between 900 F. and 1500 F., atemperature at which substantially all of the volatile constituentspresent are distilled from the starting material and the nonwolatilenon-metallic material forms a carbonaceous residue on the metal valuesof the scrap and being below the melting point of the metal to berecovered;

discharging the heated scrap material from said furnace;

thereafter physically detaching at least the major part of thecarbonaceous residue from the discharged heated scrap material andseparately recovering the resulting material after the major portion ofthe residue has been detached and separated from the discharged heatedscrap;

immersing the recovered resulting material and any residue remainingthereon, in a fused salt bath wherein such residue is oxidized andremoved from the metal values in said scrap;

and finally recovering the cleansed metal after immersion in said fusedsalt bath.

2. The process of claim 1 wherein the scrap includes copper coated withlead and the lead is recovered as a melt, separately from the othermetal values in the scrap.

3. The process of claim 1 wherein the scrap consists principally ofcopper wire.

4. The process of claim l'wherein the scrap consists of pieces of coppercovered with plastics, rubber, resin or paper and the first heating stepconverts the organic materials to a light-weight dry coke.

5. The process of claim 1 wherein the scrap includes copper coated withtin or a tin alloy and the tin is recovered from the carbonaceousresidue separated from the metal values.

6. The process of claim 5 in which the tin is recovered by oxidation ofthe carbon in the carbonaceous residue,

5 leaving the tin as a residue.

References Cited UNITED STATES PATENTS WINSTON A. DOUGLAS, PrimaryExaminer M. J. ANDREWS, Assistant Examiner US. Cl. X.R.

